Although many avenues have been explored clinically, an effective treatment of Cystic Fibrosis (CF) remains elusive. CF has proven refractory to even vector-based gene therapy approaches. Thus, alternative strategies for the genetic correction of the CF defect must be explored. MSCs have attracted increasing attention for their potential use in cell and gene therapy because they have several appealing features including: (a) the ease of isolation;(b) high efficiency of expansion in vitro;(c) MSCs are not immortal (d) differentiation into multiple cell lineages including, airway cells;(e) receptive to gene delivery protocols;and (f) they effectively home to sites of tissue injury and repair in vivo. These diverse biologic properties make MSCs excellent candidates for the development of novel cellular and genetic therapy strategies for genetic disease that to date have been refractory to vector mediated gene therapy approaches. The goal of this proposal is the development of novel gene therapy strategies for cystic fibrosis focusing on bone marrow stromal cells (MSCs). Adult MSCs from CF patients provide the potential of performing autologous stem cell therapy, if they can be corrected by delivery of the CFTR gene and then be induced to differentiate into airway epithelial cells. Our Hypothesis is that CFTR gene-corrected MSCs isolated from CF-patients can undergo differentiation into epithelial cells of the lung and;ultimately, generate mature lung cells with normal levels of chloride transport and electrophysiology. The major focus will be to study the ability to gene-correct MSCs from CF patients and the ability of these gene corrected cells to differentiate into mature cells of the airway and lung with normal physiology. We propose to use two model systems throughout these studies to analyze differentiation and correction of the genetic deficiency. One is an in vitro air-liquid interface culture model, in which primarily isolated human airway epithelial cells are grown on a semi-permeable filter, which can be maintained for up to one year. Our second model is a human airway epithelial xenograft model. In this model, denuded rat tracheas are implanted on the backs of nude mice and transplanted with human airway cells and MSCs. This system provides a primitive airway epithelial cell differentiation environment to induce the stem cell differentiation. Additionally, once we have evidence that transduced MSCs differentiate and maintain expression of CFTR as we predict, we will investigate the role of specific MSC subpopulations (small, rapidly-dividing cells vs. large, slow-growing cells), in the epithelial cell differentiation process. These studies may permit us to focus on a subpopulation of MSCs that provide enhanced levels of engraftment, differentiation or both.